compactframework >> NetworkStream.BeginRead Blocking problem

by TW9oaXQgR3VwdGE » Thu, 11 Nov 2004 12:28:04 GMT

Hi all,

I am trying to create CLient-Server based application. Talking of just
Client application, I want to read data from the server application. For
I created a socket and a new thread that reads all the time from the server.
However, the problem is when I close the socket (from client end), my data
reader thread (created above) does not close down. In turn it keeps waiting
for some message.

After bit of struggle I noted that somehow BeginRead calls back the method
after 1 minute. At that time my piece of code exits the thread. I want to
close the BeginRead operation as soon as I close the socket. You help will
appreciated. For that purpose I am presenting you with the code that I have
managed to write.

Public Delegate Sub DisplayInvoker(ByVal text As String)

Private Const IPADD As String = ""
Private Const PORT As Integer = 5000

Private m_socketClient As TcpClient
Private m_data(1024) As Byte

#Region "Private Methods"
Private Sub connect()
Dim ipAddObj As IPAddress = IPAddress.Parse(IPADD)
Dim ipEndPointObj As New IPEndPoint(ipAddObj, PORT)
Me.m_socketClient = New TcpClient(IPADD, PORT)
Me.btnSend.Enabled = True
Me.displayText("Connected to Host " + IPADD + " at Port " +
Catch ex As Exception
Me.displayText("Socket connection failed")
Me.displayText("Reason: " + ex.Message)
Me.btnSend.Enabled = True
End Try
End Sub

Private Sub displayText(ByVal text As String)
If (text Is Nothing) Or (text = "") Then
Exit Sub
End If
Me.txtReceive.Text = Me.txtReceive.Text + vbCrLf + text
End Sub

Private Sub Send(ByVal text As String)
If Me.m_socketClient Is Nothing Then
Me.displayText("No socket connection available. Cannot send
Exit Sub
End If
If (text Is Nothing) Or (text = "") Then
MessageBox.Show("No data to send")
Exit Sub
End If
Dim bytes() As Byte = (New ASCIIEncoding).GetBytes(text)
Dim streamObj As Stream = Me.m_socketClient.GetStream()
streamObj.Write(bytes, 0, bytes.Length)
Me.displayText("Data Written: " + text)
Catch ex As Exception
Me.displayText("Sending FAILED: " + ex.Message)
End Try
End Sub

'This method is called to start reading
Private Sub BeginRead()
Dim result As IAsyncResult =
Me.m_socketClient.GetStream.BeginRead(Me.m_data, 0, 1024, New
AsyncCallback(AddressOf Read), Nothing)
Catch ex As Exception
Me.displayText("Error at BeginRead: " + ex.Message)
End Try
End Sub

Private Sub Read(ByVal asyncResult As System.IAsyncResult)
Dim intCount As Int32 = 0
intCount = Me.m_socketClient.GetStream.EndRead(asyncResult)
Me.displayText("Number of Bytes Received: " +
If intCount < 1 Then
Me.displayText("Host connection closed")
End If
Dim str As String = (New ASCIIEncoding).GetString(Me.m_data, 0,
Dim result As IAsyncResult =
m_socketClient.GetStream.BeginRead(m_data, 0, 1024, New
AsyncCallback(AddressOf Read), Nothing)
Catch ex As Exception
Me.displayText("Error READING: " + ex.Message + " " + Now())
End Try
End Sub

Private Sub disconnect()
If Me.m_socketClient Is Nothing Then
Me.displayText("No socket connection")
Exit Sub
End If

Me.displayText("Manually connection closed at " + Now())
Catch ex As Exception
Me.displayText("Socket Closing Failed: " + ex.Message)
End Try
End Sub
#End Region

Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As
System.EventArgs) Handles MyBase.Load
End Sub
Private Sub btnSend_Click(ByVal sender As System.Object, ByVal e As
System.EventArgs) Handles btnSend.Click
End Sub
Private Sub btnClose_Click(ByVal sender As System.Object, ByVal e As
System.EventArgs) Handles btnClose.Click
End Sub
Private Sub btnEnd_Click(ByVal sender As System.Object, ByVal e As
System.EventArgs) Handles btnEnd.Click
End Sub
Private Sub btnConnect_Click(ByVal sender As System.Object, ByVal e As
System.EventArgs) Handles btnConnect.Click
End Sub

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BeginRead/EndRead doc implies the callback will execute and block on EndRead until data is available

"Your callback method should implement the EndRead method. When your application calls BeginRead, the system will use a separate thread to execute the specified callback method, and will block on EndRead until the provided NetworkStream reads data or throws an exception.

Testing this shows the callback is executed only when data is available; ie: if no data is received on the socket, the callback is not called. When EndRead is called within the callback, it returns immediately with the number of bytes read. The implication is also that EndRead will never block if the callback is only executed when data is available..

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Is this a known discrepancy in the doc and the real behavior is what we observed in our test

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